This invention relates to gyroscopic instruments and more particularly to apparatus for reducing gyro activation time.
The most accurate single degree of freedom gyroscopes and pendulous integrating gyro accelerometers utilize a spinning wheel encased in a "can" which in turn is floated or made neutrally buoyant by being contained in a flotation fluid within the can so as to minimize torque uncertainties caused by accelerations. The "can" or as it is more commonly known, "float" is additionally suspended by passive electromagnetic apparatus to locate the float at a consistent equilibrium position inside the case to prevent solid contact with the instrument's outer housing or case. The gyro case contains components including a module which indicates the float's angular orientation within the case and one which provides torque to maintain the float at a constant angular reference position within the housing. In this way, the torque required to maintain the float at a constant angular reference orientation within the case is a measure of the angular rate of the gyro about its input axis. The float, utilizing its spinning element, thus senses angular rate as a torque. Consequently, spurious torques that are non-rate induced provide an erroneous indication of rate and are therefore undesirable.
The suspension of the float ideally prevents changes in torques caused by float/case coupling by maintaining the float at a constant equilibrium position relative to the case. Because the suspension forces, if changed, result in spurious torques in themselves, it is desirable to limit these suspension forces to the minimum required to hold constant float position under benign conditions. To provide benign conditions, gyros are generally maintained at a constant temperature during operation.
During gyro shut down, however, the float is not maintained in its operating equilibrium position. Fluid contraction within the case, float buoyancy changes, and lack of suspension force all combine to allow the float to move from its equilibrium position. During warm-up, the float is pulled by the passive electromagnetic suspension into its equilibrium position. While the float is moving to its equilibrium position, spurious torques cause an undesirable rate indication or error which is called "drift uncertainty". There is a strong correlation between this undesirable drift uncertainty and float position away from the equilibrium position. Several hours are typically required to bring the float into its equilibrium operating position.
It is an object of this invention, therefore, to provide apparatus which significantly shortens the time required for the float to attain its equilibrium position.
Another object of the invention is such apparatus which utilizes existing gyro hardware.
It is yet another object of the invention to provide apparatus for shortening activation time which is simple, inexpensive and easy to manufacture.